The invention relates to a method for producing or assembling a fitting, such as a valve or stopcock.
U.S. Pat. No. 4,101,113 discloses a fitting with a rotating body in the form of a conical plug inside a housing, which can be produced according to such a method. A shaft that is guided to the outside through a cover connected to the housing of the fitting, which is configured as a valve, is integrally connected to the rotating body to form a single piece. The housing comprises a contact surface for an annular surface of the cover. Said contact surface is surrounded radially on the outside by an annular collar by means of which the cover is centered in relation to the housing. An annular gap is provided between the outer surface of the shaft and an inner surface of the cover surrounding the shaft in which a sealing element is arranged which fits tightly against the inner surface of the cover on the one hand and the outer surface of the shaft on the other. The sealing element is axially clamped between two thrust rings. The one thrust ring contacts the outer surface of the shaft and the other thrust ring the inner surface of the cover. Pressure is applied to the sealing element by means of a locating ring, which partially engages with said annular gap, and an axial end face of the rotating body is supported via a support ring, which is also arranged in the annular gap. Further, a secondary sealing element is provided in the form of a membrane or packing disk, which is clamped radially on the outside between the housing and the cover and is fixed radially on the inside between the support ring and said axial end face of the rotating body. The support ring is centered in relation to the shaft by means of two centering rings and is provided with an outwardly facing annular shoulder. A relatively large distance to the inner surface of the cover is specified. Precise centering of the cover in relation to the shaft is not provided. The housing comprises a comparatively soft bushing made of plastic, particularly polytetrafluoroethylene (PTFE), which serves to float-mount the rotating body and to prevent metallic contact between the rotating body and the housing. The rotating body contains a passage opening in such a way that the passage can at least partially be unblocked or blocked depending on the momentary rotary position around the axis of rotation of the rotating body. Since said bushing compensates tolerances of the inside dimensions of the housing, the axis of rotation does not usually coincide with the housing axis in such a float-mounted rotating body or plug.
Further, U.S. Pat. No. 4,462,458 discloses a fitting with a float-mounted rotating body in the form of a conical plug, which is integrally connected to a shaft to form a single piece. A sealing element, which tightly fits against the outer surface of the shaft, is clamped between the cover and the housing. The housing comprises a contact surface associated with the cover, which is provided radially outside of an annular collar to center the cover in relation to the housing. The axial position of the rotating body within the housing is secured by the cover and a thrust ring. Further, sealing forces are transmitted to a secondary sealing element, e.g., a metal or molded membrane. The cover partially rests on the sealing element and is centered within the housing by means of said annular collar. The sealing element is under direct load, and the radial alignment of the sealing element in relation to the shaft is essentially determined by the position of the cover and a centering ring arranged within the cover. Due particularly to the bushing, which is made of a comparatively soft material, and manufacturing tolerances, it has to be assumed that the axes of the housing, the rotating body and the cover do not coincide.
To rotate the rotating body, such fittings are often equipped with drives, which are typically mounted to said cover by means of brackets and are centered especially on a centering collar of the cover. Due to the offset of the axes between the rotating body and the cover and/or said bracket or the drive, lateral forces may result, which act on the rotating body and lead to leakage as well as premature wear of said bushing and/or secondary sealing element. Furthermore, due to the form-fit and positive, interlocking connection between the cover, the secondary sealing element and the housing, it cannot be excluded that the driving forces to be transmitted have a negative effect on the sealing forces of the secondary sealing element, or that the sealing forces cancel each other out at least partially, with the consequence of unacceptable external leakage.
U.S. Pat. No. 4,930,748 (=EP 353,521) discloses a fitting of this type embodied as a stopcock, the rotating body and shaft of which are made as two parts and are suitably coupled to transmit a rotary motion. This two-part configuration of shaft and rotating body makes it possible to compensate a design or manufacturing-related offset of the axes of the rotating body, the housing, the cover and the shaft. But this involves additional, not insignificant manufacturing and assembly costs.
Accordingly, it is an object of the invention to provide a method for producing a fitting that is simple to execute and that obviates the aforementioned drawbacks.
It is also an object of the invention to provide a method of assembling a fitting in which various secondary parts, especially the bushing, the secondary sealing element, the cover and optionally a drive to rotate the rotating body, are arranged in a functionally reliable manner in such a way that they are mounted centered or coaxially and are free from transverse or lateral forces with respect to the axis of rotation of the float-mounted rotating body.
These and other objects of the invention are achieved by the method described and claimed hereinafter.
The proposed method, despite a simple yet functional design, ensures the centered or coaxial arrangement of the different secondary parts in relation to the axis of rotation of the float-mounted rotating body, so that lateral forces on the secondary parts are avoided. During production or assembly of the fitting, the cover with its flat annular surface is first positioned directly against the likewise flat contact surface of the housing. No centering means for the cover in relation to the housing are provided. The cover is then centered in relation to the shaft and thus the axis of rotation of the rotating body by means of a mounting sleeve, the inner surface of which fits against the outer surface of the shaft without play and which comprises centering means that correspond to the cover, or by means of a centering ring, which is arranged within the cover and fits against the outer surface of the shaft. Since the shaft and the rotating body form a single piece, the cover is coaxially aligned in relation to the axis of rotation of the rotating body, irrespective of the position of the axis of rotation in relation to the housing axis. A drive of the rotating body that can be connected to the cover is thus also centered in relation to the axis of rotation and undesirable lateral forces are thereby avoided. The sealing element, which contacts the shaft and furthermore is arranged between the cover and the housing, preferably does not lie under direct load, which results in an exclusively nonpositive connection between the cover and the housing. When the fitting is assembled, the sealing element contacting the shaft is centered, so that spot-type wear and/or irregular wear over the circumference of the sealing element is avoided and a long service life and functionally reliable seal is ensured.
In one advantageous embodiment, the thrust ring, which is arranged in a recess of the cover, is used as a centering body, wherein an elastic element and/or an additional sealing ring, particularly in the form of an O-ring, ensures radial support of the centering body within said recess in the cover. Between the centering body and the cover, preferably along a cylindrical inside wall thereof, there is an annular gap, so that the centering body does not directly contact the cover. Instead, the annular gap is bridged by means of said elastic element and/or sealing ring and the centering body is indirectly supported inside the cover. The centering body comprises a supporting surface in such a way that the secondary sealing element is supported at least in radial direction. The centering body is configured in the form of a ring and serves as a thrust ring for the rotating body so that the latter is pushed in axial direction into the bushing of the housing at a predefined axial bias or prestressing force. The ring, which is simultaneously configured as a thrust ring and acts as a centering body, thus performs a dual function and while requiring a minimum amount of material and space ensures that on the one hand the float-mounted rotating body is axially pressed into the bushing and on the other hand the secondary sealing element is centered.
The fitting, through the housing of which a flow medium can flow, can be configured especially in the form of a stopcock, a selector valve or a control valve with a rotating body configured especially as a plug or a ball, or in the form of a butterfly valve or control flap whose rotating body is configured as a valve disk which is float-mounted within the housing. The rotating body is used to control, particularly block, throttle or regulate the flow of the flow medium. No special mounting of the shaft within the cover is necessary and the production and assembly costs are reduced. The connection between the cover and the housing is such that advantageously none of the sealing parts lie directly under load. For assembly, this allows free radial mobility and alignment of the cover and especially of the sealing elements in relation to the rotating body, and the cover is advantageously metallically supported on the associated contact surface of the housing. None of the sealing parts, particularly the primary and secondary seals, lie under direct load and the driving forces have no influence on them. During assembly, the cover is centered by means of the shaft, which is extended through the bore in the cover, by using a mounting sleeve or a centering ring that is provided in the cover, so that the shaft axis precisely coincides with the axis of rotation of the rotating body or with the plug axis. Direct loading is effected via the cover, which is fixedly connected to the housing.
Neither the cover nor the housing contains any centering means that correspond with one another, such as annular shoulders, centering surfaces, grooves or the like. The cover is flat along the contact surface, or the corresponding contact surface of the housing, so that a centered alignment of the axis of rotation or the plug axis may be readily performed even if the axis of rotation of the shutoff device is not precisely aligned with the housing axis. Said housing axis is defined by the geometry of the seat for the shutoff device in the housing. The shutoff device is supported in said bushing, which is made of a material that is soft compared to the material of the housing, and forms the axis of rotation or the plug axis, which need not coincide with said housing axis as a function of design or production. The secondary parts, particularly the cover and the secondary seals, delta ring, molded and steel membranes as well packing gland parts associated with the plug shaft are advantageously centered by means of the plug shaft. The cover as well as said molded and steel membranes can advantageously be radially shifted on associated contact surfaces of the housing for the purpose of coaxial alignment in relation to the axis of rotation or the plug axis with respect to which the shaft axis is precisely coaxial or identical. Preferably, the sealing parts do not lie under direct load.
Additional preferred embodiments of the invention are described in the following detailed description.